(1) Field of the Invention
This invention relates to a system and method for the inspection of defect detection wafers and transferring the defect data to different production wafer types.
(2) Description of the Related Art
It is important to be able to identify defective portions of integrated circuit wafers during the processing of the wafers. Inspection systems, particularly automatic inspection systems which can identify and locate such defects are of considerable interest.
U.S. Pat. No. 5,649,169 to Berezin et al. describes a method and system for declustering defect data in cooperation with wafer scanning tools. This declustering allows the system to remove noise in defect data caused by wafer scratches and the like.
U.S. Pat. No. 5,479,252 to Worster et al. describes a laser imaging system used to analyze defects on semiconductor wafers that have been detected by defect detection systems.
U.S. Pat. No. 4,845,558 to Tsai et al. describes a method and apparatus for inspecting repeating pattern devices. Data is resolved from selected pixels and directly compared either to data obtained from corresponding pixels or a data base.
Defect identification systems are often used to monitor integrated circuit wafers for defects during the fabrication process. FIG. 1 shows a schematic view of a projection system used to project mask patterns on a wafer being processed. The key elements of such a system are a light source 10, a condenser lens 12, a mask having the pattern to be projected 20 and held in place by a mask holder 14, an objective lens 16, and a wafer holder 18 holding the wafer 22 being processed. An objective lens holder 26 and a condenser lens holder 24 hold the objective lens 16 and the condenser lens 12 in place. It is possible for foreign particles to become attached to the wafer holder 18, or wafer stage, resulting in defective wafers. To monitor for these types of defects defect detection wafers are periodically processed through the projection system and analyzed for defects. If the analysis of the detect detection wafer shows that defects have occurred, the production wafers processed between that defect detection wafer and the previous defect detection wafer must be carefully inspected for defects.
FIG. 2 shows a schematic view of a conventional system for inspecting the defect detection wafers for defects. FIG. 2 shows a defect detection wafer under inspection 22 being held in place on a movable wafer holder 34, a moveable objective lens 32 held in place by a movable lens holder 36, and an image detector 30, such as a CCD camera. The movable objective lens 32 and the movable wafer holder 34 are moved relative to each other so that the objective lens scans the entire surface of the defect detection wafer 22. The output of the objective lens 32 is directed to the CCD camera 30 and a visual display 31 so that the image of the wafer surface can be observed for defects. If defects are found on the defect detection wafer then the production wafers processed between this defect detection wafer and the previous defect detection wafer must be carefully inspected for defects.
One of the problems that occur with this method of defect detection and inspection is that the defect detection wafer and the production wafers are usually quite different. Usually many different types of production wafers are processed between successive defect detection wafers. This problem can be better understood with reference to FIGS. 3 and 4. FIG. 3 shows a top view of a defect detection wafer 22a showing a number of chip sites 50 and a defect 52 occurring on the wafer. FIG. 4 shows a top view of a production wafer 22b showing chip sites 54 and the defect 52 occurring on the same location on the wafer. Although the defect 52 is in the same location on the production wafer 22b as on the defect detection wafer 22a, the locations do not appear the same because of the difference in the patterns on the defect detection wafers and on the production wafers. This difference in patterns make it difficult for operators to locate defects on production wafers based on information from defects on defect detection wafers, especially if the defects are subtle.
It is a primary objective of this invention to provide a system that translates defect information from defect detection wafers to production wafers so that the production wafers can easily be inspected for defects.
It is another primary objective of this invention to provide a method to translate defect information from defect detection wafers to production wafers so that the production wafers can easily be inspected for defects.
These objectives are achieved by providing an image memory in which image data of production wafers can be stored. The output of the image detector, such as a CCD camera or CCD scanner, is fed to an image processor unit which is connected to the image memory. The output of the image processor is fed to an image display. When the inspection of a defect detection wafer identifies a defect the image processor can select image data for a particular production wafer and superimpose the image data for the production wafer on the image data for the defect detection wafer. The image display will then display the image of the defect as it will appear on the production wafer. Operators or automatic inspection equipment can then easily inspect production wafers for the defect.